Severe Hair Loss - Need Help!

I have no idea what has caused my hair loss. it's severe. I'm almost bald. it started with a small quarter size circle in top of head and progressively got worse. It went in like a pattern around my entire head. At first, I didn't pull my hair, but for last year I've noticed that I'm pulling some of it out. Honestly, it makes my scalp feel better, sometimes it's itchy, sometimes it's not. Sometimes my scalp is sensitive to hot water. I've also noticed for about past year, there is alot of ingrown hairs on scalp.